1. Field of the Invention
The present invention relates to an apparatus for manufacturing a semiconductor device and a method for using the apparatus. More particularly, the present invention relates to a wafer stage including an electrostatic chuck, and to a method for dechucking a wafer using the wafer stage.
2. Description of the Related Art
Semiconductor devices are manufactured after performing many processes such as depositing a material layer on a wafer, patterning the deposited material layer, and removing unnecessary residuals on the wafer. To perform these processes repeatedly, a wafer is loaded on a wafer stage inside a chamber, the wafer is processed, and then unloaded.
In order to successively process a wafer, it is very important to chuck and fix the wafer in the chamber and to dechuck the wafer so that the wafer will not be damaged after processing. As semiconductor devices become highly integrated, the design rule becomes smaller, and the process margin becomes narrower. As a result, there is a greater need to chuck and fix the wafer without damaging the wafer during dechucking.
Methods for fixing the wafer to the wafer stage in the process chamber when the wafer is loaded on the wafer stage include using hardware structures such as clamps, using a vacuum to suction the rear side of the wafer (a vacuum chuck), using gravity, and using a piezoelectric effect. Various methods are available for dechucking the fixed wafer on the wafer stage after processing the wafer. The dechucking method used is chosen in accordance with the method used for fixing the wafer.
The most widely used method for fixing a wafer is the piezoelectric effect. In this method, an electrostatic chuck is used to fix the wafer, and the electrostatic chuck and a lifting means are used to dechuck the fixed wafer.
FIG. 1A illustrates a sectional view of a method for chucking a wafer using an electrostatic chuck according to the prior art. Referring to FIG. 1A, first, the structure of an electrostatic chuck 10 will be described, and then, a method for chucking a wafer 20 will be described. The electrostatic chuck 10 includes an upper insulating layer 2, an electrostatic electrode 4, a lower insulating layer 6, and a lower electrode 8. The lower electrode 8 controls the reaction speed of plasma when plasma is generated in the chamber (not shown). The electrostatic electrode 4 is connected to a DC generator (not shown), and positive charges or negative charges are distributed on the electrostatic electrode 4 by the DC generator. The electric charges on the electrostatic electrode 4 induce an electrostatic field such that the wafer 20 is chucked or dechucked. The electrostatic electrode 4 and the lower electrode 8 are insulated by the lower insulating layer 6, and the wafer 20 and the electrostatic electrode 4 are insulated by the upper insulating layer 2.
In a method for dechucking the wafer 20 according to the prior art, the wafer 20 is put on the electrostatic chuck 10, and an electrostatic field is induced by supplying power to the electrostatic electrode 4 under the upper insulating layer 2 on the upper surface of the electrostatic chuck 10. Positive charges accumulate on the electrostatic electrode 4 connected to the external DC generator (not shown), and negative charges accumulate on the lower surface of the wafer 20 by plasma generated on an upper portion of the wafer 20, thereby inducing an electrostatic field between the wafer 20 and the electrostatic electrode 4. When the upper surface of the electrostatic chuck 10 is completely in contact with the wafer 20, a clamping force is produced by the electrostatic field, and thus, the wafer 20 is chucked.
Meanwhile, some of the charges on the electrostatic electrode 4 of the electrostatic chuck 10 flow into the upper surface of the electrostatic chuck 10 through the upper insulating layer 2, and as time goes by, the electric charges accumulate. The clamping force between the wafer 20 and the electrostatic chuck 10 increases due to the accumulated electric charges. As a result, the magnitude of the clamping force grows larger than the voltage applied to the electrostatic electrode 4 of the electrostatic chuck 10. The wafer 20 and the electrostatic chuck 10 are stuck together by the increased clamping force when the wafer 20 and the electrostatic chuck 10 are dechucked.
FIG. 1B illustrates a sectional view of a method for dechucking a wafer 20 using an electrostatic chuck according to the prior art. When the wafer 20 is chucked, plasma formation on the upper portion of the wafer 20 stops, and the voltage supplied to the lower electrode 8 and the electrostatic electrode 4 of the electrostatic chuck 10 is turned off. As a result, the electric charges flow out and the clamping force is reduced. However, since a discharge time is necessary for the charges to flow when the clamping force is reduced, the wafer 20 becomes stuck to the electrostatic chuck 10.
When lift pins 12 are raised to dechuck a wafer 20 that is stuck to the electrostatic chuck 10, the force applied to the wafer 20 can easily damage the wafer 20. In order to prevent the sticking phenomenon, power is again supplied to the electrostatic electrode 4, in which positive charges remain, and negative charges flow into the electrostatic electrode 4. That is, electric charges having a charge opposite to those supplied to the electrostatic electrode 4 during chucking flow into the electrostatic electrode 4 during dechucking in order to neutralize the electrostatic electrode 4, thereby easily dechuck the wafer 20.
Subsequently, the lift pins 12 of the lifting means (not shown) are raised, and the wafer 20 is dechucked. However, in the method for supplying electric charges having an opposite polarity to the electrostatic electrode 4, the wafer 20 still possesses electric charges, and thus, the method is not of much help for dechucking.